Electric-arc-furnace plant.



THGYE E. EDWIN, BLEGTRIG'ARG FURNACE PLANT, APPLIOATI'ON FILED JUNE 26,191

will" that the current in each arc contributes to is true.

ETNAR TROYE AND EMIL EDWIN, OF CHRISTIANIA, NORWAY, ASSIGNORS TO NORSKHYDRO-ELEKTRISK KVAELSTOFAKTIESELSKAB, OF CHRISTIANIA, NOR'W'AY.

ELECTRIC-ARG-FURNACE PLANT.

To all whom it may concern Be it known that we, EINAR TROYE an EMILEDWIN, subjects of the King of Norway, both residing at Christiania,Norway, have invented certain new and useful Improvementsin-Electric-Arc-Furnace Plants; and we do hereby declare the followingto be a full, clear, and exact description of the invention, such aswill enable others skilled in the art to which it appertains to make anduse the same, reference being had to the accompanying drawings, and toletters or figures of reference marked thereon, which form a part ofthis specification.

This invention relates to electric furnace plants of the kind, where thepower is utilized for several arcs in a multiphase system, for exampleseveral arcs or furnaces of the Birkeland type.

By the transmission of power to plants with are furnacesit is veryimportant, that the furnaces have the connection affording the greateststability'because it is in this way that the best security of serviceand earning capacity is attained, while at the same time the necessarytransforming of tension may be carried out with the best possibleeconomy and with the simplest possible apparatuses. Both these objectsare attained by the present invention, which is the result of extensiveexperiments and theoreti-' cal researches, and which will be bestunderstood by means of .the following considerations: It-is known that,in any electric system all changes will be counter-acted by forces,which are created bythe change itself. When it is considered therefore,that the stability of an electric arc is due to the forces whichcounter-act the sudden changes which are produced in the arc current bymeans of exterior influences it will be evident that with regard to thefirst harmonic of the current it is important to placethe whole of theelectric system obtained by the connection in such relation ofdependence that all links of the system are utilized for the stabilizingof every separate link viz.

the stabilizing of all' the other. arcs in the system. The current curveof the arc approa'ch'es always to a certain degree' the sinusoid, andall the higher harmonics in the tension curve will therefore be idle. Asthese will accordingly l'essen'the total power factor, it is importantto limitthelh as far as Specification of Letters Patent.

Application filed June 26, 1914. serial No. 347,510.

Patented Dec. 29, 1914.

' possible and then to localize them so that their eifecton the circuitor mains will be the smallest possible. For this reason and at the sametime because they contribute 1 probably to a very great extent to theinterlor. stability of the arc the higher tension-' harmonics should belocalized to the arc to which they belong and be prevented from beingtransmitted to the electric circuit.

.1 The above considerations which have not yet to the knowledge of theapplicants been taken up in literature make the foundations for theconnections forming the present invention.

The objects of this invention with respect to the connection of the arcsare: To put the several links in depending connection with regard to thefirst harmonic of the current and make them independent of each otherwith regard to the higher harmonics of ten- SlOIl. N ow it appears thatwith regard to the connection of the arcs, the symmetrical multiphasesystem with star connection with or without a neutral capable of beingswitched oft satisfies best the requirements with regard to the current,as

the several links therefore being in direct dependence of each other.The second requirement withregard to the tension must this'connection,and. this can not only be obtained by means of a choking transformer(hedgehog transformer), but also by means of choking coils generally,whereby the connection described in the following is obtained: By theuse of a choking transformer therefore be satisfied within the scope ofone has also the advantage, that if the 0on ditions require a highermain tension, the necessary transforming down of this ten- S1OI1 may beperformed by the choking trans- 1 is a diagram showing a Birkelandfurnace in each phase connection of a three phase transformer andconnected to a neutral wire.

Fig. 2 is another diagram, in which the furnaces are in inductioncircuits. a modification of Fig. 2, where a pluralityof furnaces aresupplied with induced cur- 'rent from the sameprimary winding or coil.

Fig. 3 is a diagram illustrating the use of choking coils.

In a three-phase system the connection 4 may be carried out, so that thefurnaces,

.viz. thearcs are connected in mesh. However according to the aboveconsiderations the connections as shown on Figs. 1, 2 and 3 on theaccompanying drawing in connectionor not with a neutral would be the.

most advantageous system not only with regard to the stability but alsowith regard to regulating, security of service, and n this case alsowith regard to the transforming. It is evident from the above,'that inthe following examples the word furnacemay also be adapted to one ormore arcs ina furnace, so that the system may be used as well for theconnection for instance of three furnaces, each having one or more arcs,as forthe connection of three arcs within the same furnace.

, It should be noted, that the diagrams have been made as simple aspossible, but that also connection in parallel may be used. Also inDiagram 2 the furnaces or the arcs may be connected as shown on Fig. 2where for each transformer one may have two or more furnaces-or arcs.

The three phase system aifords certain advantages technically, while.the multiphase system affords the advantage thata change in one of theseveral links of the system causesa comparatively smaller retr,o

this connection the neutral is formed by a 4:. Means tions.

action on the totalsystem, so that the stabilizing will be better. Forsimplicitys sake the accompanying diagrams are carried out. asthree-phase systems.

On Fig. 1 a is a three phase choking transformer and b are the furnacesor the arcs of the Birkeland type, which are connected in star, havingalso a neutral point in the. choking transformer. The primary coil ofthe choking transformer may be connected in mesh or instar accoiding tothe condi- In this condition the independence of the higher harmonics oftension are attained thereby that the high reactance 'of the chokingtransformer prevents the oscillations of tension created in each linkfrom penetrating to the other furnaces connected ,to the system, whileit is evident that dependence in the first harmonic of thecurrent mayalso be attained. The same object is attained in Fig. 2, where thethree-phase choking transformer is divided into three single phasechoking transformers 0. By

Fig. 2" is special transformer 0, which may be con structed with orwithout increased induction..

In Fig. 3 the connecting conditions for the arcs have been. attainedwithout choking.

transformers by means of choking coils, the requirements for the currentbeing obtained as before, while the requirements for the tension areattained by inclosing theoscillations of tension between parts of thereactance necessary for stabilizing and limiting them to" the arcitself; The furnaces or the arcs are indicated by b as before, while aindicatesparts of the stabilizing reactance. This'fsystemof connectionmay also be useful in other furnace connections as it lessens the dangerof a puncture in the furnace. Choking-coil here indicates any kind ofreactance.

By the connection shown it is not'possible in all conditions to startthe furnaces without a connection between the star point of the furnaceand the neutral of the system.

prising a plurality of arcs in combination with an electriccircuitincluding said arcs; means to-transform'the tension supplied to saidarcs, a reactance 'in said circuit, a neutral pointin' mains of saidcircuit, and 'an electrical connection between said neutral point andthe star points of the furnace system.

2; Means for stabilizing a plurality of arcs comprising a multiphasecircuit including said arcs, means to supply multiphase current tosaidcircuit, reactance in said circuittune'd to pass only. the firstharmonic of the current, and a neutral electric return connection'commonto all the arcs.

- 3. Means for stabilizing a plurality of arcs comprising a multiphasecircuit including said arcs, means to supply multiphase current to saidcircuit, said circuit having reactance tuned to pass on the firstcurrent harmonic of each are, a grounded neutral metallic returnconnection and means in said connection between the arcs and the supplymeans for said arcs to interrupt the neutral metallic return, wherebythe arcs become interdependent with respect to the firstihar monic only.I

for stabilizing a pluralityjiof mo arcs comprising a multiphase circuit,a multiphase'transformer in said circuit, an arc in each phaseconnection to said transformer, and a neutral connection between theneutral point of the transformer and the star points of the arc.

5. Means for stabilizing a plurality of arcs comprising a multiphasecircuit, an are for each phase connection of said circuit,

and each phase connection having reactance turned to pass only the firstharmonic of the current, a transformer connected'to said circuit and agrounded metallic neutral connection common to all the phase connectionsand connected to the neutral point of the transformer. i

7. Means for stabilizing a plurality of arcs comprising a multiphasecircuit, an are for each phase connection of said circuit, and eachphase connectionhaving reactance tuned to pass only the first harmonicof the current, a transformer connected to said circuit and ametallicneutral connection common to all the phase connections and connected tothe neutral point of the trans former, and a switch in said metallicconnection whereby the neutral point of the furnacesmay be madeindependent of the neutral point for the phase connections.

.8. Means for stabilizing a plurality of arcs comprising a multiphasestar circuit, each phase connection supplying an are, re: actance meansin each connection in which the arcs are interposed in series said meanstuned to pass only the first harmonic of the current, a grounded neutralmetallic connection common to said phase connections and the neutralpoint for said phase connections, and a switch in said metallicconnections between said arcs andsaid neutral point. r,

In testimony that We claim the foregoing as our invention, We havesigned our names in presence of two subscribing Witnesses.

EINAR TROYE. EMIL EDWIN. Witnesses:

H. GUTToRMsnN, RUTH Lmns'rnom.

